This invention relates to a process for preparing N-phosphonomethylglycine by the dealkylation of an N-alkyl-N-phosphonomethylglycine. More particularly, the invention relates to a relatively simple method whereby N-phosphonomethylglycine is produced in high yield and yet relatively free of reaction by-products.
N-Phosphonomethylglycine, known also by its common name glyphosate, is a highly effective and commercially important phytotoxicant useful in controlling a large variety of weeds and crops. It is applied to the foliage of a very broad spectrum of perennial and annual grasses and broad-leafed plants. Industrial uses include control of weeds along roadsides, waterways, transmission lines, in storage areas, and in other nonagricultural areas. Usually glyphosate is formulated into herbicidal compositions in the form of its various salts which retain the anionic form of glyphosate in solution, preferably in water.
Because of its commercial importance, many processes for making glyphosate have been published. One process for the manufacture of glyphosate is described by Hershman in U.S. Pat. No. 3,969,398. In said process iminodiacetic acid is reacted with formaldehyde and phosphorous acid to produce an intermediate N-phosphonomethyliminodiacetic acid. This intermediate is oxidized to produce glyphosate.
Another process for the manufacture of glyphosate is described by Gaertner in U.S. Pat. No. 3,927,080. Gaertner describes the production of glyphosate wherein N-t-butyl-N-phosphonomethylglycine or its esters are hydrolyzed under acidic conditions.
The chemistry of the carbon/nitrogen bond of amines has been the subject of study in recent years. For example, Murahashi and Watanabe disclosed the metal catalyzed reaction of tertiary amines with water in an article entitled "Palladium Catalyzed Hydrolysis of Tertiary Amines with Water" published in the Journal of the American Chemical Society, 101, 7429 (1979). In this publication it was reported that catalytic oxidation of tertiary amines proceeded generally and efficiently with palladium catalysts to provide secondary amines and carbonyl compounds.
In European Patent No. 0,055,695, there is disclosed a process for splitting off a substituent group from the nitrogen atom of an N-substituted N-phosphonomethylglycine by hydrogenolysis. The N-substituent is described as a 1-arylalkyl group suitable for hydrogenolytic cleavage. The hydrogenolytic process is carried out in the presence of a catalyst, such as platinum or palladium on barium sulfate.